[Python-ideas] PEP 505 (None coalescing operators) thoughts

[MRAB]

On 2015-10-01 19:50, Random832 wrote:
> On Thu, Oct 1, 2015, at 14:36, MRAB wrote:
>> It's _not_ guaranteed that there'll be an exception if a is None; None
>> does have _some_ attributes.
>
> Well, it hasn't got a "d" attribute, but point taken. However, wanting
> to build expressions like this that will sometimes operate on the
> attributes of None and other times operate on the attributes of the
> non-None object normally expected to be present seems like an
> *extremely* obscure thing to want.
>
>> 'and' and 'or' don't escape parentheses. I'd take it as a general rule
>> that short-circuiting doesn't escape parentheses.
>
> Sure they do. In what way is (a and b) and c different from a and b and
> c? Heck, (a and b) and (c and d) even compiles to the same bytecode as
> other groupings [demonstrating it has the same actual semantics] *even
> though it is a different AST*. But even if it didn't, it would just be
> jumping to another jump opcode.
>
If a is falsy, it short-circuits "a and b".

The parenthesised expression returns a falsy result.

That falsy result then short-circuits "(a and b) and c".

It happens to show the same behaviour as "a and b and c" and can be
optimised to that.

Well, that's my opinion, anyway!

> It doesn't escape being mixed with a different kind of expression, which
> is sometimes accomplished with parentheses, but that's not really the
> same thing.
>